Morphological analyses

What are morphological analyses?

Morphological analyses allow insight in the size and shape of animals. In the 4-Oceans project, we aim to use information on the size and shape of the taxa of interest to get insights into their past relationship with humans and the environment. Specifically, differences in sizes and shapes of a taxon between geographical regions and chronological periods will provide more information on local adaptation, niche partitioning, and the effects of exploitation strategies employed by humans in the past.

Schematic illustrations of walrus mandible from dorsal and lateral view

Methodology

Two different approaches will be employed complementary in the project.

Linear morphometrics

Photo taken by Brenna Frasier.

This method uses traditional caliper-based measurements. These measurements are determined beforehand and have to be taken precisely on faunal remains in collections. Once all measurements are collected, groups of specimens can be compared using principal component analysis. This technique is easy and accessible, but is limited by the available measurable points on an object.

Geometric morphometrics

Spinning 3D model of a walrus skull with tusks.

This method allows more in-depth size and shape analyses. In the project 3D geometric morphometrics will be used. To get 3D data, a portable 3D light scanner (Einscan HX) is used to scan faunal remains in museum collections. On the 3D models, landmarks can be placed on specific predetermined positions using specific software. The relative position of these landmarks can then be analysed, using for example principal component analysis, to compare groups of specimens. While this approach requires specialised hard- and software, it allows for a more detailed assessment of the size and shape of animals compared to linear morphometrics.

Case studies

These techniques will be applied in two specific case studies, one focusing on the Atlantic Walrus (Odobenus rosmarus rosmarus), and the other on Pacific Parrotfish (Scaridae).

Walrus case study

Question

Walruses have been heavily exploited during the last 2000 years for their ivory, blubber and meat. This has resulted in severe population decreases with even local extinctions as a consequence. Such intense exploitation could have impacted the size and shape of walruses due to direct selection by humans or via indirect effects in the ecosystem, as humans have impacted more than only walruses. However, it is unclear if such changes have happened, and if this might further impact their modern-day conservation. Within the project, we aim to quantify any differences in the size and shape of walruses between geographical regions and chronological periods.

Walrus remains from hunting in Svalbard, in the collections of the Natural History Museum Bergen, as evidence of past exploitation.

Method

Measurements and 3D scans of modern and archaeological walrus skulls and lower jaws are collected from museums in Europe and North-America. Skulls and lower jaws were selected as the size and shape of these elements are highly linked with diet and carry the tusks, which were one of the reasons for exploitation. The first aim will be to describe age and sex determination to allow identification of archaeological material. With the obtained scans and understanding of walrus ontogeny, it will then be possible to assess differences between regions and time periods. The results of the morphological analyses will be combined with those from stable isotope analysis and aDNA to provide more in-depth analysis of local dietary analysis between walrus populations.

Image showing the differences between a male and female walrus mandible. The male mandible is wider and more bulky compared to the female one.

Lower jaws of male (left) and female (right) walruses showing sexual dimorphism.

Parrotfish case study

Question

Parrotfish are and have been a commonly consumed group of fish species on the Hawaiian Islands. These fish play crucial roles in reef systems. They have a specific diet, feeding on algae and corals, for which they have highly adapted jaws. Remains of their typically shaped jaws have been uncovered in many archaeological sites, alongside many other fish and other marine animal remains. It is unclear whether marine exploitation on the Hawaiian Islands during the last 1000 years has severely changed the fish diversity and health of the local reef systems. Parrotfish can be used as a proxy for changes in the reef system, as different species of parrotfish are adapted to specific food items.

Palenose/common parrotfish Scarus psittacus, photographed by François Libert (CC BY-NC-SA 2.0)

Method

This study will assess the impact humans had on parrotfish trophic ecology and diversity by direct exploitation and indirect alterations of the reef ecosystem. By analysing the species with traditional osteology and ZooMS and the size of parrotfish using their remains found in archaeological sites, a direct sign of overfishing could be detected through time if present. Using geometric morphometrics on their jaws and stable isotope analysis, insight into the diets of parrotfish can be obtained. By combining these techniques, the timing of human impact on the reef system, economic shifts, and climatic changes can be assessed, which can help to assess modern day conservation efforts.

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